First, we established the culture method for the embryos as early as day 5.5 embryos. We found that DMEM supplemented with 75% rat serum worked better than 100 % rat serum for E5.5 embryos whereas 100 % rat serum works better for E5.75 embryos. We are underway to optimize the condition to achieve the Cre-dependent gene disruption by Cre plasmids, since infection of recombinant Adenovirus for Cre was not sufficient enough to delete BMP receptors during cultivation. The knowledge that will be acquired through this research may give us better understanding for the primitive and definitive hematopoiesis.